Mosquito Species Linked to Tropical Diseases Detected Again in Jackson County

White City, Oregon- Aedes aegypti mosquitoes have been discovered again in Jackson County, a year after Oregon health officials announced the species had been found in the state for the first time.

The Oregon Health Authority (OHA), Jackson County Vector Control and Jackson County Public Health confirmed the identification as part of routine mosquito surveillance.

Emilio DeBess, D.V.M., state public health veterinarian in OHA’s Public Health Division, said the repeat appearance of Ae. aegypti is a concern because the species has typically been found in warmer climates of the United States, Southeast Asia, Africa and the Pacific Islands.

“These mosquitoes have been known carry and transmit diseases that are more typical to warmer climates, such as Zika virus, chikungunya, dengue and yellow fever,” DeBess said. These viruses spread to humans through the bite of an infected mosquito, he said.

The mosquitoes become infected when they bite and feed on someone carrying the virus. They primarily feed during the day and prefer to feed on humans.

Still, DeBess emphasized that the risk of these infections to local residents remains low. “Acquiring these diseases depends on the presence or arrival of someone who is currently infected with one of the diseases after infection outside the United States,” he said. “As was the case when Ae. aegypti mosquitoes were first found in Oregon in 2024, there have been no reports of anyone having acquired viruses associated with Ae. aegypti from within the state.”

Routine mosquito surveillance in Jackson County monitors different species and tests for diseases such as West Nile virus and Western equine encephalitis, which are more common in the Culex mosquito genus. The program also helps officials determine human risk and implement control strategies.

Adult Ae. aegypti mosquitoes are relatively small and are marked by black-and-white patterns, with white or silver scale patches on their legs and body. The species likely originated in Africa and has since spread globally through trade and shipping.

Unlike other mosquitoes, Ae. aegypti cannot fly far—only about 500 feet. They prefer warm, wet weather and often live in or near homes. Officials say climate change is enabling the species to expand into the western United States.

Geoff Taylor, manager of Jackson County Vector Control, said prevention remains key. “Many prevention methods that work for other types of mosquitoes apply to Aedes aegypti,” he said.

Recommended steps include dumping or draining standing water around homes, removing containers that collect water, repairing leaky outdoor faucets, cleaning gutters, and covering or screening rain barrels and trash bins. Officials also recommend wearing mosquito repellent and using mosquito nets when sleeping outdoors or in unscreened rooms.

DeBess said the discovery highlights the importance of ongoing trapping efforts. Identification and monitoring “gives state and local agencies advanced warning on the potential spread of a species so they can take steps to reduce health risks in the population,” he said.